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1. Draw the structure of the unknown ester product and name using the IUPAC system. Why must the neutralization be performed in ice? Compare your 'H NMR with the NMR provided for the pure ester, what conclusions can be drawn from this comparison?
Why must the Compare your 1H NMR with the NMR provided for the pure ester, what conclusions can be drawn from this comparison?
Experiment # 17 Raspberry Beret Introduction Low molecular weight esters are used in the fragrance, flavor, and pharmaceutical industries. The condensation of carboxylic acids and alcohols is the most common synthetic route to ester formation, however this requires a strong acid catalyst. In this lab, esters from an unknown alcohol will be esterified with acetic acid, using an acidic resin catalyst. The ion exchange resin used in this lab is a polymer that contains sulfonic acid groups, which can substitute for sulfuric acid. After the reaction, the resin can be filtered off, washed, regenerated with 2 M HCl, and re- used. Shown below is the esterification of isobutanol with formic acid to give isobutyl formate, which exibits the odor of raspberry. H You got you + OH A microscale apparatus will be used in this experiment to minimize the use of materials. Since esterification is a reversible process, a Hickman still will be used to remove the water that is formed. Fortunately, acetic acid has a higher boiling point than water, and does not form an azeotrope with water. Different esters will have different fragrances. After your reaction, waft the vapors of your product to your nose to determine its smell. You may determine the starting alcohol based on the smell of the product. To test your hypothesis, gather consensus from your classmates on the smell. It is agreed upon that whoever makes the raspberry scent must dance to Prince's 1985 hit song "Raspberry Beret" at the end of the lab period, however anyone may join in. You may need to smell coffee or get some fresh air to clear the sensory cells in your nose so as not to confuse the odors. For safety, never smell the esters directly, and remove yourself from the lab should you feel dizzy. As a final test of your hypothesis, obtain an NMR of your oil. Locate the acetate CH3 peak, which should integrate to 3 H's. Procedure a Weigh and transfer resin beads (0.20 g) to a clean, dry microscale vial. In a fume hood, add 1 mL of your unknown alcohol and glacial acetic acid (4 mL). Add a boileezer chip and assemble a reflux apparatus with a Hickman still , making sure that the still has a septum. Gently heat the mixture to reflux, and continue to reflux for 20 min. Let the mixture cool. Pipette the liquid from the Hickman still into a test tube. Pipette the liquid from the reaction pot into the same test tube, making sure that none or very few resin beads are transferred. Add petroleum ether (2 mL) to wash the beads and pipette the Greener Organic Experiments 102

liquid into the test tube. Rinse the reflux apparatus with acetone and discard the wash in the organic waste container. Place the re-usable resin beads in the labeled beaker in the fume hood, you may use acetone to facilitate the transfer. Add water (2 mL) into the test tube to obtain two layers. If two layers do not separate, add water 1 mL at a time. Using a pipette, transfer the top layer into a new test tube. To this new test tube, add cold 10% NaOH (2 mL) to neutralize any remaining acid. Mix and check with a pH paper that it is basic. Using a dry glass pipette, transfer the top layer into another dry test tube that has been pre-weighed. Do not transfer any of the bottom layer, which contains water, into the new test tube. To remove the petroleum ether, use a clamp or a test tube holder to immerse the tube sideways over a beaker of boiling water (~20-40 min). Heat the test tube gently to evaporate off the petroleum ether. Any trace of petroleum ether could result in extra protons in the 1H NMR spectrum. Allow the test tube to come to room temperature before obtaining the mass of the product. Waft the vapors of the product to your nose and propose a structure of the unknown alcohol based on the table below. Obtain the 1H NMR spectrum of your product and integrate the signals. Purification is not performed in this experiment, and your NMR may show extraneous peaks. Obtain the NMR of the pure unknown ester from your instructor after showing evidence of your own crude NMR. Confirm the structure of your unknown and fill in the reagents table in your notebook. Unknown Alcohol Smell of Ester Product n-butanol banana, sour apple isobutanol banana, apricot, butter, pineapple, rum, strawberry sec-butanol sweet, solvent-like, banana t-butanol camphor, blueberry n-pentanol pears Isopentanol banana cyclohexanol fruity, sweet, musty, solvent-like 1-hexanol fruity, green apple, banana peel 1-heptanol apricot, fatty, wine, wood 1-octanol fruity, orange sec-octanol fruity benzyl alcohol sweet, floral, jasmine, fresh, gardenia, and ylang-ylang

Moss - Acetic Acid Vip (4.1.05 g/cm 3 ) massa 180 butand movs - v.p(* 1.0.2016 glemy = MW-m Mal 1000 1021 Post-Lab Discussion Identity of Unknown_Ammo Unknown # raspberry Percent Yield _ 62.32 First determine the identity of the unknown based on smell and the 'H NMR, then fill in the stoichiometry table below and calculate the percent yield. Ester Acetic Acid 4.2 Alcohol 0.806 Substance Mass (0) MW (g/mol) Mmol Equivalents 60.0.52 69.94 70.81 10.87 1 1 Draw the structure of the unknown ester product and name using the IUPAC system. Why must the neutralization be performed in ice? Compare your 'H NMR with the NMR provided for the pure ester, what conclusions can be drawn from this comparison? izobutyl formate (2-methylpropyl methanoate -CH3 CH₃